ExifTool is a mature, comprehensive Perl library and command-line application for reading, writing, and manipulating metadata across hundreds of file formats (images, audio, video, documents, archives, etc.). It supports all major metadata standards (EXIF, IPTC, XMP, GPS, ICC profiles, maker notes) and many proprietary formats. The architecture is modular: each file format has a dedicated Perl module under `lib/Image/ExifTool/` that implements a consistent interface for reading and writing metadata. The core `Image::ExifTool.pm` provides the API and CLI entry point. The codebase is exceptionally well-documented, with auto-generated HTML tag reference pages and extensive test coverage (over 100 test scripts with golden output files). It is actively maintained by a single author (Phil Harvey) with frequent releases. While the library is tightly coupled to the ExifTool framework, individual format modules follow clean patterns and could serve as reference implementations for metadata parsing. The repository also includes reusable utilities like `File/RandomAccess.pm` for buffered random file access and `Image/ExifTool/Geolocation.pm` for reverse geocoding.